F1: Mercedes reveal main fear as Lewis Hamilton battles Max Verstappen

Mercedes remain fearful that a "catastrophic" engine failure in the final five races could derail their championship fight against Red Bull Racing. The lack of faith in their power units is the reason Valtteri Bottas has taken more engine penalties than any other driver on the grid this season.

The Silver Arrows have established themselves as the most reliable on the power unit front in the Hybrid Era, but 2021 has seen them fall behind all the other engine manufacturers. The Mercedes powered teams have taken more power unit components, which has resulted in multiple grid penalties this season.

The lack of reliability has left Mercedes struggling to push outright in their battle with Red Bull. They continue to fear a potential engine failure going into the final five races of the campaign, and are aware that any DNF, especially for Lewis Hamilton, is likely to end his hopes for an eighth Drivers' championship title.

Bottas took his sixth new power unit at the United States Grand Prix, that is three more than permitted for the season. Hamilton is currently on his fourth and Mercedes are hoping he will not require a fifth, which will trigger yet another grid penalty and dent his hopes of overhauling the 12-point deficit to Max Verstappen in the title race.

"The reason is that we are balancing performance versus reliability to the end of the season," Mercedes' chief strategist James Vowles said, as quoted on Fox Sports. "One failure to finish a race, be it because of a chassis or Power Unit fault, would be catastrophic for the championship and as a result of that, we are managing that in the best way possible to the end of the year."

Vowles is hoping that the sixth internal combustion engine (ICE) will help Bottas until the end of the campaign without further grid penalties. He also believes the Finn will enjoy better performance from the new components in the final five races of the campaign.

"In the case of Valtteri, that meant taking one further ICE to make sure we had absolutely the best compromise," he added. "As to whether it improved [Bottas'] performance, yes a small amount but it's more about the balance across the remainder of the season rather than one event.